The conventional stator structure of motor has defects of magnetic leakage phenomenon and inaccurate positions of upper and lower poles. Please refer to FIG. 1 showing a stator of a prior art. The stator consists of piled silicon steel sheets 101 and the arms of silicon steel sheets are T-shaped that four groups of coils are twined around them. The costs for the stator and twining coils are very expensive.
In order to improve the defects described above, a scheme of forming poles by using a pair of coils had been adopted. Please refer to FIG. 2 which includes two pole layers (upper and lower) 201, a magnetically conductive cylinder 203 and a pair of coils 202. Two ends of the magnetically conductive cylinder 203 is tightly engaged with the hollow of two pole layers 201 having a insulator therebetween. The insulator is twined by a pair of coils 202. During engaged process, two pole layers are positioned which is complementary to each other in order that every pole is well distributed in a ring by a mechanical angle. In spite of its low cost, the scheme is not good enough because a crack 204 generated therewith will influence the magnetic conduction.
In order to avoid a crack which may affect the magnetic conduction and to avoid the need of matching the upper and lower pole layer, it is necessary to make a simple and stable stator for improving the efficiency of the motor.